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No description available.

No description available.

Polymer – clay nanocomposites have improved thermal, mechanical, and barrier properties when compared with the pure polymer. The objective of this study was to examine if gas separation performance could be improved by introducing a layered nanopourous aluminum phosphate with a large aspect ratio into a polymeric matrix. The aluminum phosphate has eight membered rings, which could potentially serve as a size selective medium. A hexafluorinated polyimide, 6FDA-6FpDA-8%-DABA, was used as the polymeric matrix. The polyimide and the aluminum phosphate were synthesized separately according to well documented procedures. The two materials were blended and fabricated into nanocomposite membranes. The effect of mixing temperature and percentage of layered aluminum phosphate added to the polymer on the permeation properties were examined. These factors had a direct effect on the degree of intercalation and exfoliation of the nanocomposite structure. Transmission FTIR, TEM, DMTA, and X-ray diffraction were used to characterize the morphology, structure, and composition of these nanocomposite films. The permeation properties of the nanocomposite membranes were evaluated using pure gases (He, O₂, N₂, CH₄, CO₂) at 35°C and a feed pressure of 4 atm. In general, the permeability decreased and the selectivity coefficients increased when adding 10 wt% aluminum phosphate to the polyimide. Furthermore, the membranes showed size selectivity, consistent with the pore size in the layered aluminum phosphate. / Master of Science

Les besoins en électronique de puissance, de plus en plus exigeants, ont motivé des recherches à l'échelle mondiale sur d'autres matériaux tels que le diamant comme remplaçant du silicium. Nos travaux de recherche sont plus spécifiquement axés sur la définition et la qualification de matériaux polymères capables de garantir l'intégrité des fonctions physiques de modules de puissance en environnement sévère. L'étude concerne la durabilité de candidats polymères à retenir pour le boîtier dont l'objectif est de protéger l'interrupteur de l'environnement extérieur. Suite aux choix des différents polymères étudiés, variables dans leur chimie et leur morphologie (amorphe ou semi-cristallin), un premier objectif scientifique est alors de chercher les relations structures/propriétés permettant de contrôler le procédé de mise en forme des polyimides semi-cristallins et d'en déduire les conditions requises à l'obtention de performances optimisées. Un second objectif a concerné la tenue des différents matériaux sélectionnés en vieillissements isothermes thermo-oxydatifs. / Requirements in power electronics are more and more demanding about materials behavior in their operating conditions. This has motivated global scale researches about other materials replacing silicon such as diamond. This study is specifically focusing on the definition and qualification of polymer materials which could preserve physical functions of power modules in severe environments. This study focuses on the durability of several polymers used for the case. This later allows to protect the chip from external environment. The choice of different studied polymers which are dissimilar in chemistry and morphology (i.e. amorphous or semicrystalline) has been made in this study. Then, a first scientific goal was to search the structures/properties relations leading to the control of the manufacturing process of semicrystalline polyimides. A second goal concerned the mechanical strength evaluation of selected materials after thermo-oxidative isothermal ageing.

Mechanical Rubbing still is an useful alignment method in this time. In this study, we investigated the surface wettability of rubbed polyimide(PI) thin film. By using contact angle measurements, we found the surface free energy have strong connection with surface roughness in different rubbing times. We also discussed the wettability of rubbed PI thin film in parallel and anti-parallel of rubbing direction. We found that if we rubbed PI thin film 3 times in 0.3mm depth then the structure of SSFLC is more uniform than the alignment effect of other rubbing times and we found that the values of polar energy in parallel and anti-parallel of rubbing direction are very close. In the other part of study, we degenerated the polyimide before coating. We found that the reflection anisotropic spectrum(RAS) have a blueshift and the rubbing strength will be more influential in the wettability of PI thin film than the film with no degenerate process.

Les composites à matrice organiques (CMO) et fibre de carbone sont de plus en plus employés dans la réalisation de structures « tièdes » (aubes de fan, nacelles …) ; ces pièces peuvent être soumises, en service, à la fatigue mécanique, au cyclage thermique et à la fatigue thermo-mécanique. Bien qu’il existe une littérature consistante sur le comportement en fatigue des composites tissés, l'interaction entre fatigue et la dégradation liée à l'environnement à haute température n’a pas été encore bien exploitée. Le couplage entre les effets de la thermo-oxydation, le comportement mécanique (viscoélastique, viscoplastique) de la matrice organique à températures élevées et la dégradation par fatigue peut être néfaste pour le composite.Le but de ce travail est de caractériser et de modéliser - pour les composites tissés C/matrice organique - le comportement thermomécanique, l'apparition et le développement de l’endommagement liés aux mécanismes mécaniques cycliques (fatigue) sous environnement contrôlé (température et gaz).Une étude préliminaire sur un composite stratifiée [02/902]s a été menée pour pouvoir analyser les effets de l’environnement sur une architecture simple. La corrélation d’image numérique (CIN) et des scans μ-tomographiques (μCT) ont été employés pour le suivi et la caractérisation de l’endommagement de fatigue de composites tissés 2D à architecture complexe pour applications aéronautiques. Les effets de l’environnement sur la dégradation par fatigue ont été également explorés.L'objectif à long terme de cette étude est de fournir des outils expérimentaux et numériques pour renforcer la compréhension et la modélisation du couplage mécanique/endommagement/environnement pour la prédiction de la durée de vie et pour la proposition de protocoles d’essais accélérés réalistes de pièces « tièdes » en CMO. / In the next future, the employment of organic matrix/carbon fibre composites (OMC) is foreseen for the realization of “hot” structures: these parts may be subjected, in service, to mechanical fatigue (e.g. fan blades turbo-engines), thermal cycling and thermo-mechanical fatigue (e.g. aircraft structural parts). Though there is a consistent literature concerning the fatigue behaviour of woven composites, the interaction between fatigue and environmental degradation at high temperature has been poorly explored. Coupling between thermo-oxidation effects, mechanical (viscoelastic, viscoplastic) behaviour of the polymer matrix at high temperatures and degradation due to fatigue may be highly detrimental for the material. This work aims at characterizing and modelling - for carbon fibre/organic matrix (polyimide) textile composites – the thermomechanical behaviour, the onset and the development of damage related to cyclic mechanical mechanisms (fatigue) under controlled (temperature and gas) environment.A preliminary study on a cross-ply laminate [02/902]s has been carried out in order to analyse the environmental effect on a model sample. Digital Image Correlation (DIC) and μ-Computed Tomography (μCT) have been used to monitor and characterize the fatigue damage of 2D woven composites for aeronautical applications. The environmental effect on fatigue degradation have been also explored.The long-term aim of the study is to provide experimental and numerical tools to strengthen the understanding and the modelling of mechanics/damage/environment coupling for durability prediction.

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International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The Microelectronics and Computer Technology Corporation (MCC) has developed a rapid turn around process for fabricating multichip modules (MCM’s) called the Flexible Manufacturing of MCM’s (FMM). The Army Research Lab (ARL) in co-operation with the Applied Physics Laboratory (APL), has investigated the survivability of this technology in high-g applications. Comparisons were made to other packaging technologies by constructing a 3-channel digital recorder in this and two other competing technologies.

The rapid development of polymer nanocomposites has received extensive attention over the last few decades. The ability to alter functionalities of composites, dramatically improving properties and performance at low filler content creates flexibility in designing materials for advanced applications in various industrial fields. This work focuses on nanocomposites relevant to the packaging and aerospace industries. This work evaluated the ability to homogeneously distribute nanomaterials into a polymer matrix, understand the effects on rheological properties, understand changes to microstructure and effects, and characterize properties of resulting nanocomposite. High torque melt mixing was used to disperse surface modified cellulose nanocrystals in a poly(lactic acid) (PLA) resin and graphene in a phenylethynyl terminated imide resin, PETI 298, using bulk graphite. Rheology, Raman spectroscopy, and X-Ray powder diffraction were applied for the understanding of changes to the microstructure and location of optimum loading by the determination of the percolation threshold. Thermomechanical performance was evaluated through TGA, DMA, and DSC. It was determined that graphene and short stacks of graphene could be dispersed and distributed at low loadings in PETI 298. As expected, the addition of graphitic material led to an increase in viscosity, but also caused a retardation of the cure which could be attributed to increased viscosity or quenching of free radicals. Changes to the microstructure were difficult to evaluate because of the competing chemistry occurring in the system but it could be determined that something significant occurs around 1 wt % at which the melt rheology and the microstructure behavior was different from other composites. It was further determined that the melt mixing process led to the formation of an ordered structured. Modification of the cellulose nanocrystals (m-CNC) with Cardura, glycidyl ester, provided no improvement to mechanical properties of PLA composites. However, m-CNCs were found to nucleate the crystallization of PLA. Lack of improvement to mechanical properties could be attributed to the degradation of polymer during processing.